Magnetic amplifier circuit



Aug. 25, 1953 KER 2,650,342

MAGNETIC AMPLIFIER CIRCUIT Filed Feb. 25, 1952 Inventor.-

y @i Mm His Attorney.

Patented Aug. 25, 1953 MAGNETIC AMPLIFIER CIRCUIT Montgomery Ker, Scotia, N. Y., asslgnor to General Electric Company, a corporation of New York Application February 23, 1952, Serial No. 273,095

3 Claims.

This invention relates to magnetic amplifier system, and more particularly to magnetic amplifiers having feed-back windings for affecting the output of the magnetic amplifiers.

The principal object of this invention is to provide a simple and eflicient means for varying the amplification and, hence, the output current of a magnetic amplifier.

Other objects, features and advantages of my invention will be apparent from the subsequent detailed description of a preferred embodiment thereof, while the scope of the invention is set forth in the appended claims.

In carrying out my invention in one form, I provide a magnetic amplifier comprisin a saturable core reactor having a pair of load windings supplied from a source of alternating current, and a pair of control or saturating windings. One of the control windings is utilized for partially saturating the core of the saturable reactor and thereby atfecting the alternating current passing through the load windings. The other control windin is utilized as a feedback winding for supplying selectively positive, negative or zero feedback. The second control winding is energized by being connected between the sliders of a pair of potentiometer resistors. These potentiometer resistors are connected in parallel, and arranged to carry direct currents proportional to the current through the load windings by being connected to a bridge rectifier in circuit with the load current. The second control vinding, as a result, provides a feedback which is positive, negative or zero depending on the relative settings of the sliders of the two potentionieters.-

This invention is described and illustrated herein in connection with a simple saturable reactor type magnetic amplifier. but it will in understood that it is equally applicable to nth a:- magnetic amplifiers, such as the self saturating type, for example.

For a clearer and more detailed understanding of the invention, reference should be had to the accompanying drawing in which the single figure is a diagram of an electrical circuit embodying the invention.

Referring to the drawing, there is shown an automatic current regulatin system for a direct current generator, which system embodies the magnetic amplifier circuit of this invention. The generator, which is designated by the numeral it, supplies current to an external load (not shown) through a pair of armature terminal conductors H and 12. A shunt I3 is connected in circuit with conductor l2 for reasons which appear hereinafter.

The generator I0 has a suitable excitation circuit which is represented diagrammatically by the winding H. This winding may be energized by an exciter I5 which, as illustrated, is directly mechanically connected to the shaft of generator III for operation in synchronism with the generator. Also as illustrated, exciter I5 is of the self-excited type having an excitation winding l6 for supplying excitation thereto.

The armature current from generator It may be regulated to maintain it at a predetermined value by means of a regulator H which controls the excitation of exciter I5 and through this exciter the excitation of generator [0. Regulator H, as illustrated, includes a carbon pile l8 connected in series with exciter excitation winding l6, and a pivoted lever 19 arranged to vary the compression on carbon pile I 8 and thereby to vary the resistance of this carbon pile, in a well known manner. The carbon pile may be biased toward the compressed or minimum resistance position by a tension spring 20, while an electromagnet device 2| having an energizing winding 22 may be arranged to attract an armature 23 mounted on lever l9, the-pull exerted by electromagnet 2! on armature 23 opposing spring 20 and tending to move carbon pile l8 to the decompressed or maximum resistance position.

As shown, the coil 22 of the regulator is supplied with alternating current which is approximately proportional to the current through shunt 13, through the medium of a magnetic amplifier circuit 24. This circuit 24 includes a saturable core reactor 25 having a pair of alternating current load windings 26 and 21, and two unidirectional current control windings 28 and 29. Saturable core reactor 25 is shown diagrammatically, and this device may take any conventional form such as a three-legged laminated core, for example, with the two load windings wound on the two outer legs and the two control windings on the center leg. Connections 39 and 40 are provided for the load windings to a source of alternating current (not shown) which may, for example, be a conventional source of cycle cur rent. The current passing through the load windings 26 and 21 is utilized to energize control winding 22 of the regulator, such current passing also through suitable intervening connections such as It and 42 and through a rectifier device 30 which is illustrated as a bridge type rectifier having four half-wave unidirectional conducting devices 3|. Devices 3| are preferably of the'dry -ometers including winding 22.

type and substantially identical in characteristics.

The load windings 2| and 21 are connected to terminals 82 and 88 of bridge rectifier 80 which terminals may be referred to'as the alternating voltage terminals. Connected between the other two terminals 14 and 35 of rectifier 80, which may be referred to as the direct current terminals, is a pair of potentiometer resistors 8t and II, the circuit from terminal 34 to the potenti- Potentiometers 88 and 81 preferably are substantially identical as to their total resistance and the increments of resistance provided by moving their respective slides 86a and 31a. The two sliders 38a and 31s are connected respectively to the terminals of second control winding 29.

The first control winding 28 is connected to b energized by the voltage drop across shunt l3. which voltage drop is proportional to the current flowing through conductor l2.

The operation of the regulating system shown in the drawing is as follows.. A signal voltage is derived from shunt l8, which signal voltage is proportional to the current in armature conductor i2 to be regulated and maintained at a predetermined value. This signal voltageis amplifled by magnetic amplifier 24 as a result of the effect of control winding 28 on saturable core reactor 25. The signal voltage produces a current in the control winding 28 which partially saturates the reactor 25, and this partial saturation permits a predetermined amount of alternatin current to flow through load windings 26 and 21. This predetermined amount of current energizes operating winding 22 of the regulator. This attracts armature 23 with a force sufilclent partially to counteract the effect of spring 28 and maintain the resistance of carbon pile I! at a certain value. The resistance of the carbon pile l8 under this condition is just enough to permit sufllcient excitation current to flow in excitation winding Ii of the exciter IE to generate enough excitation voltage to excite excitation winding ll of the generator sufilciently to maintain the current in conductors I I and i2 at the desired value.

Assume now, for purpose of illustration, that a slight increase in the current conductors H and i2 occurs, raising this current above the value which is desired to maintain. This increase, by

increasing the signal voltage derived from shunt l3, increases the saturation of'saturable core reactor 25. This increases the alternating current flowing through reactor 25 which increases the pull exerted by device 2| on armature 23. This, in turn, reduces the compression on carbon pile l8 and increases the resistance of this carbon pile, which reduces the current in exciter excitation winding i and consequently reduces the voltage of exciter i5. reduces the excitation of generator l0 until the resulting reduction in the armature current output of the generator reduces the current in conductors Ii and i2 to the desired value and equilibrium is restored.

A reduction in the generator output current flowing in conductors H and i2 below the desired value results in the opposite operation of the regulating system to that described in the preceding paragraph, and the consequent increase of the current to the equilibrium value.

My invention provides a desirable and useful position of the slider of one .potentiometer providing a certain potential, there is 9, corresponding position of substantially equal potential on the other potentiometer. When the two sliders are positioned in such equal potential positions, no current flows in control winding 29. If either of the potentiometer sliders is moved from its equal potential position, however, so that the potentials of the two'sliders are unbalanced, current fiows in winding 2!. Such current produces a magnetomotive force which opposes the magnetomotive of winding 28 for one direction of movement of the slider. and produces an additive magnetomotive force for the other direction of movement of the slider. Therefore, by relative movements of sliders I! and 21a, either positive, negative or zero feedback can be obtained. When the sliders 36a and 81a are at equal potential positions, zero feedback is provided, while positive or negative feedback 'is provided when the sliders are not at equal potential position, the feedback being positive when the magnetomotive force of winding 2! adds to that of winding 28 and negativewhen the magnetomotive force of winding 29 opposes or bucks that of winding 28.

With this arrangement, if it is desired to maintain less output current from generator II, the feedback is increased positively, i. e., one or both of sliders 86a and 31a are moved so that the feedback becomes either less negative or more positive. This increases the output of magnetic amplifier 24 for a particular signal voltage from shunt l3. This increases the pull on armature 23 and pivots arm is to reduce the compression of carbon pile l8 and increase the resistance across this carbon pile. This reduces the armature voltage of exclter IS, with a resulting reduction of the excitation of generator III. This reduces the output current of generator l0 until equilibrium is restored at a new value smaller than the value previously maintained by the regulating system.

If it is desired to increase the generator current held by the regulating system, one or both of the sliders 38a and 31a are moved so that the resulting voltage and current fed back to windin 29 are more negative than previously, viz., produce a greater opposing efi'ect on winding 28 than previously. This has the opposite efi'ect of that just described and results in the holding of a arrangement for adjusting the generator output larger generator armature output current.

My invention provides a magnetic amplifier circuit which greatly increases the range over which a particular saturable core reactor may be operated, or looking at it another way, it makes possible the use of a much smaller saturable core reactor in a particular circuit. It will be understood also, by those familiar with feedback circuits, that in the positive feedback range the sensitivity of the magnetic amplifier and hence the sensitivity of the regulator is increased, while in the negative feedback range the stability of both is increased. In a current regulating system such as that illustrated in Fig. 1, this means that the sensitivity is increased for smaller values of current while the stability is increased for larger values'of current, and both of these conditions are very desirable in such a regulating system.

It will be understood that my invention is not limited in its usefulness to the particular current regulating system illustrated and described herein. It will be readily apparent, for example, that it could be applied with equal facility to a voltage regulating system, inasmuch as the signal appearing across shunt I3 is actually a voltage signal, being the voltage drop across the shunt produced by the current therein.

Nor is the invention limited to the particular saturable reactor arrangement illustrated. For example, a saturable transformer can be employed instead. By saturable transformer I mean a saturable core device having one or more primary alternating current windings connected to the source of alternating current and one or more secondary alternating current windings connected to the load. Such a device can be used instead of the saturable core reactor illustrated and described .herein, providing only that two control windings for affecting the core saturation are present.

It should be understood also that my invention is not limited to potentiometer devices having sliders such as those described and illustrated herein, and that other equivalent adjustable rheostatic devices may be employed, if desired. The essential requirement is that such devices be provided with adjustable tap means for deriving various selected potentials intermediate the potential applied to the terminals of the devices. Furthermore, in some cases, where only a relatively small adjustment is required, it is not necessary that both of the devices have adjustable tap means. That is, it may be possible to employ in place of one of the adjustable tap devices, a resistor having a fixed intermediate tap voltage or two fixed resistors connected in series and providing a junction of intermediate potential Therefore, while I have illustrated and described my invention in one preferred form thereof, it will be understood that modifications may be made by those skilled in the art, and I intend by the appended claims to cover all such modifications which fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A magnetic amplifier system comprising a saturable reactor having at least one load winding and two control windings, load current circuit means including connections to a load for consuming current from the said load winding, rectifier means connected in said load current circuit, a pair of parallel connected resistor devices each having tap means for deriving an intermediate potential therefrom connected to said rectifier means, the tap means for at least one of said resistor devices being adjustable to provide a plurality of intermediate potentials, said resistor devices being arranged to carry unidirectional currents proportional to the current passing through the said load current circuit, connections to a source of signal voltage for energizing one of the said control windings to affect the saturation of the said reactor and thereby affect the passage of current through the said load current circuit, and means connecting the said second control winding to the said two tap means for energization by the potential between the two tap means whereby the said second control winding affects the action of the said first control winding in affecting the passage of current through the said load current circuit by an amount dependent in sense and magnitude upon the relative positions of the said two tap means.

2. A magnetic amplifier system comprising a saturable reactor having at least one load winding and two control windings, load current circuit means including connections to a source of alternating current for supplying current for passage through said load winding and connections to a load for consuming the current passing through said load winding, unidirectional conducting device means connected in the said load current circuit, a pair of parallel connected potentiometer devices each having adjustable slider means for deriving intermediate potentials therefrom connected to said unidirectional conducting device means, said potentiometer devices being arranged to carry unidirectional currents proportional to the said current passing through the said load current circuit, connections to a source of signal voltage for energizing one of said control windings to control the saturation of said reactor and thereby regulate the amount of current passing through the said load current circuit, and means connecting said second control winding to said two adjustable slider means for energization by the potential between the two sliders whereby said second control winding affects the action of the said first control winding in controlling the saturation of said reactor by an amount dependent in sense and magnitude upon the relative positions of the two said sliders.

3. A magnetic amplifier system comprising a saturable reactor having at least one load winding and two control windings, load current circuit means including connections to a source of alternating current for supplying current for passage through said load winding and connections to a load for oonsiuning the current passing through said load winding, a bridge rectifier device having alternating current terminals and direct current terminals, means connected to the said alternating current terminals connecting the said bridge rectifier device in said load current circuit, a pair of potentiometers each having an adjustable slider for deriving intermediate potentials therefrom, said potentiometers being connected in parallel between said direct current terminals whereby said potentiometers carry unidirectional currents forming portions of the current passing through the said load current circuit, connections to a source of signal voltage for energizing a first of said control windings to partially saturate said reactor and thereby control the amount of current passing through the said load current circuit, and means connecting said second control winding to said two sliders for energization by the potential difference between the two sliders whereby said second winding affects the saturating action of the said first control winding and thereby affects the current passing through said load current circuit by an amount depending in sense and magnitude upon the relative positions of the two said adjustable sliders.

MONTGOMERY KER.

N 0 references cited. 

